1. Field of the Invention
The present invention relates to flywheel power source apparatuses, and more particularly to a flywheel power source apparatus which is effective as a power source for computers or the like, wherein continuous supply of power to a load is required during outage of a power source and even when large voltage variation occurs at the power source the voltage variation supplied to the load must be minimized.
2. Description of the Prior Art
As a result of the significant development of computer technology in recent years, computers have been introduced in the industrial field and other fields. In such a computer, if power supply to the main components, particularly a processing unit, a memory unit or the like, is interrupted due to outage or large voltage variation, the processing until then may become useless or the stored information may be lost.
Consequently, in the prior art, a flywheel power source apparatus as shown in FIG. 1 or FIG. 2 is used as a power supply compensation means during service interruption or large voltage drop. The flywheel power source apparatus in FIG. 1 and FIG. 2 is disclosed in Japanese Laid-open Applications No. 60-66632 and No. 60-197198, respectively. The flywheel power source apparatuses utilize rotational force of a flywheel rotating at a high speed, and convert the rotational energy into electric energy and supply it to a computer or the like.
FIG. 1 shows an example of a flywheel power source apparatus in the prior art. In FIG. 1, F designates a power source apparatus body. The power source apparatus body F comprises an auxiliary inverter 1, a converter 2, a changeover switch 3, a main circuit converter 4, a main circuit inverter 5, and a switching circuit 67 having a changeover switch 6 of main circuit S and a changeover switch 7 of direct voltage delivery circuit L. Numeral 8 designates an AC (alternating current) power source, numeral 9 a load, and R a flywheel device. The flywheel device R is composed of a generator/motor unit and a flywheel. The flywheel device R normally rotates the flywheel by output of the auxiliary inverter at 30,000 r.p.m. for example, and during service interruption the device converts the rotational energy of the flywheel into electric energy and outputs it.
Operation of the flywheel power source apparatus will now be described. The main circuit S composed of the main circuit converter 4 and the main circuit inverter 5 supplies AC power of constant voltage and constant frequency from the external power source 8 to the load 9 through the changeover switch 6. Then the changeover switch 3 for a compensation circuit P composed of the auxiliary inverter 1, the flywheel device R and the converter 2 is open, and the flywheel contained in the flywheel device R stores energy according to the high speed rotation by the auxiliary inverter 1.
If an abnormal state occurs in the external power source 8 due to outage or the like, the changeover switch 3 controlled by an outage detecting means (not shown) is closed, and power generation is effected in the generator by the inertial energy of the flywheel of the flywheel device R. The AC power is converted into DC power by the converter 2, and the DC power is supplied through the inverter 5 and the changeover switch 6 to the load 9.
When the changeover switch 7 is turned on, the changeover switch 6 is turned off.
In the above constitution, however, since the converter 2 and the switch 3 are required at the output side of the flywheel device, the circuit constitution is complicated and the cost becomes high.
In order to solve the above-mentioned problems, the applicant has already proposed a flywheel power source apparatus, wherein an auxiliary inverter is connected between an input/output terminal of a flywheel device and the front side of an inverter to constitute the main circuit.
FIG. 2 is a block diagram of the flywheel power source apparatus, and parts corresponding to those in FIG. 1 are designated by the same reference numerals.
In FIG. 2, numeral 10 designates a transformer, and a primary winding 10a of the transformer 10 is connected through a switch 11 to AC power source 8. A secondary winding 10b of the transformer is connected to a series circuit comprising a converter 4 of main circuit S, a chopper circuit 12, a DC (direct current) filter 13, a main circuit inverter 5 and a switching circuit 67.
The secondary winding 10b is connected to direct voltage delivery circuit L. Numeral 14 designates an auxiliary inverter, and the input stage of the auxiliary inverter 14 is connected to the joint between the converter 4 of the main circuit S and the chopper circuit 12, and the output stage thereof is connected to the input/output terminal of a flywheel device R. The auxiliary inverter 14 and the flywheel device R constitute the voltage compensation circuit P.
Numeral 15 designates a switch connected between the switching circuit 67 and the load 9.
Operation of the flywheel power source apparatus will be described. At normal state, output of the AC power source 8 is supplied to the primary winding 10a of the transformer 10 through the switch 11. Output obtained from the secondary winding 10b of the transformer 10 is converted into DC voltage by the converter 4 and further converted into constant voltage by the chopper circuit 12, and then the ripple of the DC output is removed by the DC filter 13. The DC output from the DC filter 13 is supplied to the inverter 5 and converted into AC by the inverter 5, and the AC output is shaped into a sinusoidal wave by an AC filter (not shown) and then supplied through the switching circuit 67 and the switch 15 to the load 9.
On the other hand, the DC output from the converter 4 is converted into high frequency by the inverter 14, thereby the flywheel device R is rotated at a high speed and stores energy.
If an abnormal state such as outage or voltage reduction of the power source 8 occurs, output of the converter 4 is reduced. Then the rotational energy stored by rotation of the flywheel device R is released as electric energy, and the output voltage accompanying the release is supplied to the auxiliary inverter 14. The AC voltage supplied to the auxiliary inverter 14 is converted into DC and supplied through the auxiliary inverter 14 to front stage of the chopper circuit 12 of the main circuit S.
Output supplied from the flywheel device R to the front stage of the chopper circuit 12 is supplied through the DC filter 13, the inverter 5, the switching circuit 67 and the switch 15 to the load 9.
In the above-mentioned flywheel power source apparatus in the prior art, however, since the auxiliary inverter 14 only is installed between the main circuit S and the flywheel device R, one auxiliary inverter must control voltage and frequency simultaneously and therefore the power control by the inverter is complicated.
Since the chopper circuit 12 installed in the main circuit S is normally operated, it must be designed with continuous rating.
Further, since ripple in significant amount is produced in the output of the chopper circuit 12, the DC filter 13 must be installed at the output stage of the chopper circuit 12 as above described; thereby the constitution is complicated and the cost becomes high.